(1) Field of the Invention
The present invention relates to substrate cleaning apparatus and methods for supplying a cleaning liquid from a nozzle to and cleaning substrates such as semiconductor wafers, glass substrates for photomasks, glass substrates for liquid crystal displays, substrates for optical disks and the like. More particularly, the invention relates to a technique of performing a cleaning process while moving a nozzle so that a cleaning liquid supply position on a surface of a substrate moves at least between center and edge of the substrate.
(2) Description of the Related Art
A conventional substrate cleaning apparatus of the type noted above includes, for example, a spin support mechanism for supporting and spinning a substrate, a jet nozzle for discharging a high-pressure jet of cleaning liquid under a fixed pressure, and a moving mechanism for moving the nozzle so that a cleaning liquid supply position on the surface of the substrate moves at a fixed speed at least between center and edge of the substrate.
This apparatus supplies the cleaning liquid over the entire surface of the substrate by moving the nozzle while spinning the substrate, so that the cleaning liquid supply position on the surface of the substrate moves at least between center and edge of the substrate. In this way, the substrate surface is cleaned with particles of dust and the like removed therefrom.
The cleaning liquid discharge pressure is one of the cleaning conditions that greatly influence the effect of cleaning. Thus, the discharge pressure is varied for each lot of substrates with different degrees of particle adhesion, for each type of substrate or for each individual substrate.
The above conventional apparatus has the following drawback.
The substrate in a spin moves, in a central region thereof, at low speed relative to the nozzle, and at increasing speed toward the edge. The central region of the substrate moving at low relative speed may undergo an excessive impact of the cleaning liquid. Generally, the cleaning liquid discharge pressure which is one of the cleaning conditions is set to achieve an optimal cleaning result for the central region of the substrate. With the discharge pressure selected to suit the central region, edge regions of the substrate moving at high relative speed cannot be cleaned sufficiently. Such uneven cleaning results have adverse effects on subsequent substrate treatment.
A different substrate cleaning apparatus includes, instead of the above jet nozzle, a nozzle for discharging a cleaning liquid with ultrasonic vibration of a fixed frequency. This apparatus supplies the cleaning liquid with ultrasonic vibration over the entire surface of a substrate by reciprocating the nozzle over the substrate surface while spinning the substrate at a fixed speed. In this way, the substrate surface is cleaned with particles of dust and the like removed therefrom by ultrasonic vibration.
An ultrasonic frequency or output applied to the cleaning liquid is one of the cleaning conditions that greatly influence the effect of cleaning. Thus, the ultrasonic frequency or output is varied for each lot of substrates with different degrees of particle adhesion, for each type of substrate or for each individual substrate.
This conventional apparatus also has the following drawback.
The substrate moves, in a central region thereof, at low speed relative to the nozzle, and at increasing speed toward the edge. The central region of the substrate moving at low relative speed may undergo an excessive impact of the ultrasonic vibration applied to the cleaning liquid. Generally, the ultrasonic output which is one of the cleaning conditions is set to achieve an optimal cleaning result for the central region of the substrate. With the ultrasonic output selected to suit the central region, edge regions of the substrate moving at high relative speed cannot be cleaned sufficiently. Such uneven cleaning results have adverse effects on subsequent substrate treatment.